Many types of devices for sealing or anchoring in a passage which is meant to include open or cased holes are known in the art. Some types involve mechanical squeezing of sealing elements by longitudinal relative movement which results in radial expansion of the sealing elements to close off a wellbore. One example of such a packer is a retrievable design shown in U.S. Pat. No. 5,273,109. Other designs are known as inflatables and can be advanced thru-tubing. Typical of such designs is U.S. Pat. No. 4,979,570. These designs incorporate an inflatable element generally covered by overlapping slats with one or more sleeves to act as sealing elements covering a portion of the overlapping slats.
The packers that compress annular seals longitudinally to squeeze them in the radial direction can require radial expansions as much as 10%, which necessitates considerable longitudinal or axial force. Some seals have been made hollow or porous to reduce the force required to set them. However, hollow or porous seals are subject to decrease in size or collapse as the pressure increases and, thus, are unsuitable for high ambient pressures.
One of the objects of the present invention is to overcome the high setting forces required for prior designs so that a packer or plug can be provided which requires only minimal force to engage and disengage or change the size of the seal. Another objective of the present invention is to provide a seal whose performance is unaffected by ambient pressure.
Bellows of one type or another have been used for expansion joints to compensate for thermally induced forces. U.S. Pat. No. 4,332,401 illustrates an expansion joint for casing used in injecting steam into wells. U.S. Pat. No. 5,421,241 illustrates the use of a bellows in a gas lift valve construction. U.S. Pat. No. 5,143,158 illustrates the use of bellows in a subsea wellhead apparatus. U.S. Pat. No. 5,119,861 illustrates the use of compressible elastomers to create a pipe plug. Also of interest in the general area of sealing devices are U.S. Pat. Nos. 5,348,087; 2,157,449 (Canadian); U.S. Pat. Nos. 5,303,518; 5,185,806; 5,119,861; as well as a multi-component compressible sealing member sold under the trademark HEXPAK.RTM. by Petroleum Engineering Services Inc. of Houston, Tex. This packer employs a sealing element system made of an outer elastomer membrane that is wrapped around a metal sleeve seal mandrel. An inner elastomer provides rubber pressure during pack-off to expand the seal mandrel and ensure solid pack-off state is achieved and molding to the inner casing contour is perfected.
The prior designs for seals leave unanswered the need for a sealing device which sets with low forces yet reliably seals against differential pressures, such as in downhole applications. The apparatus of the present invention employs an annular bellows as the seal element which requires minimal force to engage and disengage or change in size. One of the objects of the present invention is to allow a bellows to significantly change its diameter as compared to prior designs involving compression of elements with an axial force. Another objective of the invention is to provide a bellows that can be made from solid materials so that its performance is not affected by ambient pressures. Bellows elements can be readily stacked to achieve multiple independent sealing surfaces without additional design complexity or required increases in engagement force. Accordingly, using the bellows of the present invention, if only one of the multiple ribs which contact the outer pipe are in a pit or crack-free location, the seal becomes effective. Another object of the invention is to provide a greater seal the higher the differential pressure applied. Another objective is to minimize extrusion potential and damage by virtue of the configuration of the design, which facilitates the sealing process, even if there is misalignment of the components supporting the bellows or variability in pipe diameter. Another objective is to be able to make the bellows seal from a wide variety of materials, all of which can functionally operate due to the low engagement force required. These and other objectives will become more apparent to those of skill in the art from a review of the preferred embodiments described below.